chars.add(randomAlpha());
    }
    for (int i = 0; i < nonAlpha; i++) {
      chars.add(randomNonAlpha());
    }
    Collections.shuffle(chars, random);
    char[] array = Chars.toArray(chars);
    this.testString = new String(array);
  }

  private char randomAlpha() {
    return ALPHA.charAt(random.nextInt(ALPHA.length()));
  }

  private char randomNonAlpha() {

    public List<Character> create(Character[] elements) {
      char[] chars = Chars.toArray(asList(elements));
      return charactersOf(String.copyValueOf(chars));
    }
  }

  public static class CharactersOfCharSequenceGenerator extends TestCharacterListGenerator {
    @Override
    public List<Character> create(Character[] elements) {
      char[] chars = Chars.toArray(asList(elements));
      StringBuilder str = new StringBuilder();

    public List<Character> create(Character[] elements) {
      char[] chars = Chars.toArray(asList(elements));
      return charactersOf(String.copyValueOf(chars));
    }
  }

  public static class CharactersOfCharSequenceGenerator extends TestCharacterListGenerator {
    @Override
    public List<Character> create(Character[] elements) {
      char[] chars = Chars.toArray(asList(elements));
      StringBuilder str = new StringBuilder();

      @Override
      public Hasher putUnencodedChars(CharSequence chars) {
        for (Hasher hasher : hashers) {
          hasher.putUnencodedChars(chars);
        }
        return this;
      }

      @Override
      public Hasher putString(CharSequence chars, Charset charset) {
        for (Hasher hasher : hashers) {
          hasher.putString(chars, charset);
        }
        return this;
      }

     */
    private byte[] encodeUnicode(String s) {
        char[] chars = s.toCharArray();
        byte[] out = new byte[chars.length * 2];
        for (int i = 0; i < chars.length; i++) {
            out[2 * i] = (byte) (chars[i] & 0xFF);
            out[2 * i + 1] = (byte) ((chars[i] >> 8) & 0xFF);
        }
        return out;
    }

    /**

      chars.add(randomAlpha());
    }
    for (int i = 0; i < nonAlpha; i++) {
      chars.add(randomNonAlpha());
    }
    Collections.shuffle(chars, random);
    char[] array = Chars.toArray(chars);
    this.testString = new String(array);
  }

  private char randomAlpha() {
    return ALPHA.charAt(random.nextInt(ALPHA.length()));
  }

  private char randomNonAlpha() {

        String format;
        if (d > 0) {
            // Length 11+ chars
            format = "%d d %02d:%02d h";
        } else if (h > 0) {
            // Length 7 chars
            format = "%2$02d:%3$02d h";
        } else if (m > 0) {
            // Length 9 chars
            format = "%3$02d:%4$02d min";
        } else {
            // Length 7-8 chars
            format = "%4$d.%5$03d s";
        }

    String allMatchingChars = allMatchingChars(bitSet);
    char[] result = new char[STRING_LENGTH];
    // Fill with matching chars.
    for (int i = 0; i < result.length; i++) {
      result[i] = allMatchingChars.charAt(random.nextInt(allMatchingChars.length()));
    }
    // Replace some of chars by non-matching.
    int remaining = (int) ((100 - percentMatching) * result.length / 100.0 + 0.5);
    while (remaining > 0) {

    String allMatchingChars = allMatchingChars(bitSet);
    char[] result = new char[STRING_LENGTH];
    // Fill with matching chars.
    for (int i = 0; i < result.length; i++) {
      result[i] = allMatchingChars.charAt(random.nextInt(allMatchingChars.length()));
    }
    // Replace some of chars by non-matching.
    int remaining = (int) ((100 - percentMatching) * result.length / 100.0 + 0.5);
    while (remaining > 0) {

            assertTrue(result.startsWith("NtlmChallenge[challenge=0x"));
            assertTrue(result.endsWith(",dc=SERVER123]"));

            // Hexdump.toHexString with size = length * 2 produces 8 uppercase hex chars
            // The hex should be "010203FF"
            assertTrue(result.contains("010203FF"));
        }

        @Test
        @DisplayName("toString with empty challenge array")